It resulted in the Ritzy workers being sacked, but it is not yet clear what has happened to the employee in Hackney.

A spokesperson for the cinema firm said: “Picturehouse has recently been subject to cyber attacks on its website. A few weeks ago, an email was sent from a Bectu email address instructing employees to encourage further cyber attacks in support of strike action.

“Bectu disassociated itself from any such unlawful activity and we began an investigation into who was responsible. As a result of this investigation, we initiated a disciplinary process in relation to a few employees potentially involved.

“They will have the right to appeal against any decisions that are taken and therefore, we cannot comment further at this stage.”

Bectu, which is a branch of Prospect, disputes Picturehouse’s claims regarding the cyber attacks, with a statement on its website stating: “The reps were dismissed as a result of an email sent to union members reporting discussions at a union meeting.”

Bectu chief Gerry Morrissey said: “We believe that our reps at the Ritzy have been dismissed due to their trade union membership and activities and we will challenge these decisions in the strongest terms.

“Our reps across Picturehouse have been fighting for fair pay and for dignity at work. Our first step in supporting our reps will be to launch Employment Tribunal claims and to seek interim relief for these trade union dismissals.”

The union found support from a group of Labour MPs, including shadow chancellor John McDonnell, who wrote to The Guardian to express “extreme concerns” over Picturehouse’s treatment of Bectu reps.

The MPs urged the cinema chain to “withdraw any sacking and suspension of trade union reps and negotiate with their staff”.

Bectu members at five Picturehouse cinemas, including those in Hackney, are staging further strikes this Friday. Staff are to down tools at 3pm and join a picket line at the Crouch End venue, where guest speakers will feature as part of the demonstration.

The strike will end at 5am on Saturday.

Bectu is demanding that Picturehouse, owned by screen operator Cineworld, pays its employees the London Living Wage, which currently stands at £9.75 per hour.

A statement regarding pay on the Picturehouse website reads: “For many years Picturehouse Cinemas has paid its front of house customer service staff well above minimum wage.

“Our pay rates are amongst the highest in the industry and have enabled us to attract and retain staff who are knowledgeable about film, skilled in many areas and able to offer high levels of service.”